1. Field of the Invention
The present invention relates to a temperature-dependent switch having a temperature-dependent switching mechanism, a housing, receiving the switching mechanism, that has a lower part and an upper part made of insulating material, two stationary contacts provided on the upper part on its inner side, each of which is electrically connected to an external terminal associated with it, and a current transfer member, moved by the switching mechanism, which electrically connects the two stationary contacts to one another as a function of temperature.
2. Related Prior Art
A switch of this kind is known from DE 26 44 411 C2.
The known switch has a housing with a cup-like lower part into which a temperature-dependent switching mechanism is placed. The lower part is closed off by an upper part that is retained on the lower part by means of the elevated rim thereof. The lower part can be produced from metal or from insulating material, while the upper part is in any case produced from insulating material.
Two rivets, whose inner heads serve as stationary contacts for the switching mechanism, sit in the upper part. The switching mechanism carries a current transfer member in the form of a contact bridge, which depending on the temperature is brought into contact with the two stationary contacts and then electrically connects them to one another.
The external heads of the two rivets serve as solder terminals for conductors.
The temperature-dependent switching mechanism has, in a manner known per se, a bimetallic disk and a spring disk, through which a pin which carries the contact bridge passes centeredly. The spring disk is guided circumferentially in the housing, while the bimetallic disk is braced, depending on the temperature, either against the bottom of the lower part or against the rim of the spring disk, and thereby either allows contact between the contact bridge and the two stationary contacts, or lifts the contact bridge away from the stationary contacts so that the electrical connection between the external terminals is interrupted.
This temperature-dependent switch is used, in known fashion, to protect electrical devices from overheating. For this, the switch is connected electrically in series with the device to be protected, and is arranged mechanically on the device so that it is thermally connected thereto. Below the response temperature of the bimetallic disk, the contact bridge rests against the two stationary contacts so that the circuit is closed and power is supplied to the device to be protected. If the temperature rises above a permissible value, the bimetallic disk then lifts the contact bridge away from the stationary contact, so that the switch opens and the power supply to the device to be protected is interrupted so that the latter can cool off, whereupon the switch then automatically closes again.
Although the known switch meets a number of technical requirements, it still has a series of disadvantages which are associated with its manufacture, its installation on a device to be protected, and automatic closing after cooling off.
One disadvantage lies in the complex production of the known switch: after manufacture of the cover, the rivets must still be attached to it later. A further disadvantage is the fact that conductors must also be soldered onto the external rivet heads; this generally cannot be automated. This means, however, that manufacture of a ready-to-connect switch, packaged with conductors, is in this case time-consuming and thus costintensive.
Further disadvantages may be seen in conjunction with the installation of the known switch on a device to be protected. On the one hand, the known switch offers only solder terminals or conductors, while crimp or screw terminals are often required today. If the lower part is produced from plastic, thermal coupling to the device to be protected is relatively poor in the case of the known switch, while if the lower part is produced from metal, good thermal coupling can be implemented, but the elevated metal rim of the lower part must then often be electrically insulated from the outside.
In summary, therefore, the disadvantages with the known switch are not only the laborious, complex manufacture but also the installation possibilities on a device to be protected, which are not sufficient for many applications.
In this connection, DE 31 22 899 C2 discloses a temperature-dependent switch having a lower housing part made of metal and an upper housing part made of insulating material. Two connector tongues, the first of which is connected to a stationary contact arranged centeredly, are insert-molded into the upper part. The second connector tongue is equipped with clips which, when the upper part is installed, are electrically connected to the lower part.
Arranged in the interior of the closed housing thus constituted is a bimetallic switching mechanism that, as a function of its temperature, creates an electrically conductive connection between the stationary contact and the lower housing part, and thus between the two connector tongues.
A disadvantage with this switch is the fact that assembly, in particular the arrangement of the upper part on the lower part, is laborious, since for the purpose, the clips configured integrally with the second connector tongue must be correspondingly folded over. In the event of production errors or inaccuracies, the reliability of the electrical connection between the connector clip and the lower part is not guaranteed.
Here again, as with the switch mentioned at the outset, the elevated lower part made of metal requires lateral insulation for certain applications.
A further disadvantage of the known switch is the fact that the connector tongues project upward vertically from the upper part, which interferes with installation on the device to be protected and, in particular, with electrical connection.
A further disadvantage evident with this switch is also the fact that it automatically switches on again after cooling. While switching characteristics of this kind may be entirely sensible for protecting a hair dryer, the two switches so far described are not suitable for protecting devices that must not switch back on automatically after cooling, as may be the case, for example, with electric motors. In this connection, it is already known from many publications to equip the temperaturedependent switch with a so-called "self-hold" function, for which purpose a resistor is connected in parallel with the external terminals. After the switching mechanism opens, a low current flows through said resistor, which thereby generates sufficient heat to keep the switching mechanism above its switching temperature so that the switch does not close again automatically. This is instead accomplished by shutting off the supply voltage, so that the switching mechanism is no longer kept above the switching temperature by the current flowing through the self-hold resistor.